Wiki info about Ki-61-I hei

A lightweight multipurpose fighter plane, the Ki-61 Hien (“Swallow”) was well-armed and well-armored.
From the very beginning, the makers of the Ki-61 concerned themselves with protecting the fuel tanks and the pilot. The light multipurpose fighter was an effective answer to “hit-and-run” fighters, thanks to its survivability and high diving speed.
The Ki-61 had a Kawasaki Ha-40 liquid-cooled inverted V12 engine, a licensed copy of the DB 601A, capable of 1175 hp.
A prototype was ready in 1941, and by the next year the first production models were manufactured and the Ki-61 entered service.
To strengthen armament in the Ki-61-I, instead wing-mounted machine guns of the previous models Ki-61-1-Co and -Otsu was established by German's 20-mm cannons MG 151/20, which in the amount of 800 units in august 1943 were taken to Japan by submarines.
All in all, 3,078 Ki-61 fighters (of various types) were produced.